DESCRIPTION

File::Temp
can be used to create and open temporary files in a safe
way. There is both a function interface and an object-oriented
interface. The File::Temp constructor or the tempfile() function can
be used to return the name and the open filehandle of a temporary
file. The tempdir() function can be used to create a temporary
directory.

The security aspect of temporary file creation is emphasized such that
a filehandle and filename are returned together. This helps guarantee
that a race condition can not occur where the temporary file is
created by another process between checking for the existence of the
file and its opening. Additional security levels are provided to
check, for example, that the sticky bit is set on world writable
directories. See safe_level for more information.

For compatibility with popular C library functions, Perl implementations of
the mkstemp() family of functions are provided. These are, mkstemp(),
mkstemps(), mkdtemp() and mktemp().

Additionally, implementations of the standard POSIX
tmpnam() and tmpfile() functions are provided if required.

Implementations of mktemp(), tmpnam(), and tempnam() are provided,
but should be used with caution since they return only a filename
that was valid when function was called, so cannot guarantee
that the file will not exist by the time the caller opens the filename.

Filehandles returned by these functions support the seekable methods.

OBJECT-ORIENTED INTERFACE

This is the primary interface for interacting with
File::Temp
. Using the OO interface a temporary file can be created
when the object is constructed and the file can be removed when the
object is no longer required.

Note that there is no method to obtain the filehandle from the
File::Temp
object. The object itself acts as a filehandle. Also,
the object is configured such that it stringifies to the name of the
temporary file, and can be compared to a filename directly. The object
isa IO::Handle
and isa IO::Seekable
so all those methods are
available.

by default the object is constructed as if tempfile
was called without options, but with the additional behaviour
that the temporary file is removed by the object destructor
if UNLINK is set to true (the default).

Supported arguments are the same as for tempfile
: UNLINK
(defaulting to true), DIR, EXLOCK and SUFFIX. Additionally, the filename
template is specified using the TEMPLATE option. The OPEN option
is not supported (the file is always opened).

$tmp = File::Temp->new(TEMPLATE=>'tempXXXXX',

DIR=>'mydir',

SUFFIX=>'.dat');

Arguments are case insensitive.

Can call croak() if an error occurs.

newdir

Create a temporary directory using an object oriented interface.

$dir = File::Temp->newdir();

By default the directory is deleted when the object goes out of scope.

Supports the same options as the tempdir
function. Note that directories
created with this method default to CLEANUP => 1.

$dir = File::Temp->newdir($template,%options);

filename

Return the name of the temporary file associated with this object
(if the object was created using the "new" constructor).

$filename = $tmp->filename;

This method is called automatically when the object is used as
a string.

dirname

Return the name of the temporary directory associated with this
object (if the object was created using the "newdir" constructor).

$dirname = $tmpdir->dirname;

This method is called automatically when the object is used in string context.

unlink_on_destroy

Control whether the file is unlinked when the object goes out of scope.
The file is removed if this value is true and $KEEP_ALL is not.

$fh->unlink_on_destroy(1);

Default is for the file to be removed.

DESTROY

When the object goes out of scope, the destructor is called. This
destructor will attempt to unlink the file (using unlink1
)
if the constructor was called with UNLINK set to 1 (the default state
if UNLINK is not specified).

No error is given if the unlink fails.

If the object has been passed to a child process during a fork, the
file will be deleted when the object goes out of scope in the parent.

For a temporary directory object the directory will be removed
unless the CLEANUP argument was used in the constructor (and set to
false) or unlink_on_destroy
was modified after creation.

If the global variable $KEEP_ALL is true, the file or directory
will not be removed.

FUNCTIONS

This section describes the recommended interface for generating
temporary files and directories.

tempfile

This is the basic function to generate temporary files.
The behaviour of the file can be changed using various options:

$fh = tempfile();

($fh,$filename) = tempfile();

Create a temporary file in the directory specified for temporary
files, as specified by the tmpdir() function in File::Spec.

($fh,$filename) = tempfile($template);

Create a temporary file in the current directory using the supplied
template. Trailing `X' characters are replaced with random letters to
generate the filename. At least four `X' characters must be present
at the end of the template.

($fh,$filename) = tempfile($template,SUFFIX=>$suffix)

Same as previously, except that a suffix is added to the template
after the `X' translation. Useful for ensuring that a temporary
filename has a particular extension when needed by other applications.
But see the WARNING at the end.

($fh,$filename) = tempfile($template,DIR=>$dir);

Translates the template as before except that a directory name
is specified.

($fh,$filename) = tempfile($template,TMPDIR=>1);

Equivalent to specifying a DIR of "File::Spec->tmpdir", writing the file
into the same temporary directory as would be used if no template was
specified at all.

($fh,$filename) = tempfile($template,UNLINK=>1);

Return the filename and filehandle as before except that the file is
automatically removed when the program exits (dependent on
$KEEP_ALL). Default is for the file to be removed if a file handle is
requested and to be kept if the filename is requested. In a scalar
context (where no filename is returned) the file is always deleted
either (depending on the operating system) on exit or when it is
closed (unless $KEEP_ALL is true when the temp file is created).

Use the object-oriented interface if fine-grained control of when
a file is removed is required.

If the template is not specified, a template is always
automatically generated. This temporary file is placed in tmpdir()
(File::Spec) unless a directory is specified explicitly with the
DIR option.

$fh = tempfile(DIR=>$dir);

If called in scalar context, only the filehandle is returned and the
file will automatically be deleted when closed on operating systems
that support this (see the description of tmpfile() elsewhere in this
document). This is the preferred mode of operation, as if you only
have a filehandle, you can never create a race condition by fumbling
with the filename. On systems that can not unlink an open file or can
not mark a file as temporary when it is opened (for example, Windows
NT uses the O_TEMPORARY
flag) the file is marked for deletion when
the program ends (equivalent to setting UNLINK to 1). The UNLINK
flag is ignored if present.

This will return the filename based on the template but
will not open this file. Cannot be used in conjunction with
UNLINK set to true. Default is to always open the file
to protect from possible race conditions. A warning is issued
if warnings are turned on. Consider using the tmpnam()
and mktemp() functions described elsewhere in this document
if opening the file is not required.

If the operating system supports it (for example BSD derived systems), the
filehandle will be opened with O_EXLOCK (open with exclusive file lock).
This can sometimes cause problems if the intention is to pass the filename
to another system that expects to take an exclusive lock itself (such as
DBD::SQLite) whilst ensuring that the tempfile is not reused. In this
situation the "EXLOCK" option can be passed to tempfile. By default EXLOCK
will be true (this retains compatibility with earlier releases).

($fh,$filename) = tempfile($template,EXLOCK=>0);

Options can be combined as required.

Will croak() if there is an error.

tempdir

This is the recommended interface for creation of temporary
directories. By default the directory will not be removed on exit
(that is, it won't be temporary; this behaviour can not be changed
because of issues with backwards compatibility). To enable removal
either use the CLEANUP option which will trigger removal on program
exit, or consider using the "newdir" method in the object interface which
will allow the directory to be cleaned up when the object goes out of
scope.

Create a directory from the supplied template. This template is
similar to that described for tempfile(). `X' characters at the end
of the template are replaced with random letters to construct the
directory name. At least four `X' characters must be in the template.

$tempdir = tempdir(DIR=>$dir);

Specifies the directory to use for the temporary directory.
The temporary directory name is derived from an internal template.

$tempdir = tempdir($template,DIR=>$dir);

Prepend the supplied directory name to the template. The template
should not include parent directory specifications itself. Any parent
directory specifications are removed from the template before
prepending the supplied directory.

$tempdir = tempdir($template,TMPDIR=>1);

Using the supplied template, create the temporary directory in
a standard location for temporary files. Equivalent to doing

$tempdir = tempdir($template,DIR=>File::Spec->tmpdir);

but shorter. Parent directory specifications are stripped from the
template itself. The TMPDIR
option is ignored if DIR
is set
explicitly. Additionally, TMPDIR
is implied if neither a template
nor a directory are supplied.

$tempdir = tempdir($template,CLEANUP=>1);

Create a temporary directory using the supplied template, but
attempt to remove it (and all files inside it) when the program
exits. Note that an attempt will be made to remove all files from
the directory even if they were not created by this module (otherwise
why ask to clean it up?). The directory removal is made with
the rmtree() function from the File::Path module.
Of course, if the template is not specified, the temporary directory
will be created in tmpdir() and will also be removed at program exit.

Will croak() if there is an error.

MKTEMP FUNCTIONS

The following functions are Perl implementations of the
mktemp() family of temp file generation system calls.

mkstemp

Given a template, returns a filehandle to the temporary file and the name
of the file.

($fh,$name) = mkstemp($template);

In scalar context, just the filehandle is returned.

The template may be any filename with some number of X's appended
to it, for example /tmp/temp.XXXX. The trailing X's are replaced
with unique alphanumeric combinations.

Will croak() if there is an error.

mkstemps

Similar to mkstemp(), except that an extra argument can be supplied
with a suffix to be appended to the template.

($fh,$name) = mkstemps($template,$suffix);

For example a template of testXXXXXX
and suffix of .dat
would generate a file similar to testhGji_w.dat.

Returns just the filehandle alone when called in scalar context.

Will croak() if there is an error.

mkdtemp

Create a directory from a template. The template must end in
X's that are replaced by the routine.

$tmpdir_name = mkdtemp($template);

Returns the name of the temporary directory created.

Directory must be removed by the caller.

Will croak() if there is an error.

mktemp

Returns a valid temporary filename but does not guarantee
that the file will not be opened by someone else.

$unopened_file = mktemp($template);

Template is the same as that required by mkstemp().

Will croak() if there is an error.

POSIX FUNCTIONS

This section describes the re-implementation of the tmpnam()
and tmpfile() functions described in POSIX
using the mkstemp() from this module.

Unlike the POSIX implementations, the directory used
for the temporary file is not specified in a system include
file (P_tmpdir
) but simply depends on the choice of tmpdir()
returned by File::Spec. On some implementations this
location can be set using the TMPDIR
environment variable, which
may not be secure.
If this is a problem, simply use mkstemp() and specify a template.

tmpnam

When called in scalar context, returns the full name (including path)
of a temporary file (uses mktemp()). The only check is that the file does
not already exist, but there is no guarantee that that condition will
continue to apply.

$file = tmpnam();

When called in list context, a filehandle to the open file and
a filename are returned. This is achieved by calling mkstemp()
after constructing a suitable template.

($fh,$file) = tmpnam();

If possible, this form should be used to prevent possible
race conditions.

See tmpdir in File::Spec for information on the choice of temporary
directory for a particular operating system.

Will croak() if there is an error.

tmpfile

Returns the filehandle of a temporary file.

$fh = tmpfile();

The file is removed when the filehandle is closed or when the program
exits. No access to the filename is provided.

If the temporary file can not be created undef is returned.
Currently this command will probably not work when the temporary
directory is on an NFS file system.

Will croak() if there is an error.

ADDITIONAL FUNCTIONS

These functions are provided for backwards compatibility
with common tempfile generation C library functions.

They are not exported and must be addressed using the full package
name.

tempnam

Return the name of a temporary file in the specified directory
using a prefix. The file is guaranteed not to exist at the time
the function was called, but such guarantees are good for one
clock tick only. Always use the proper form of sysopen
with O_CREAT | O_EXCL
if you must open such a filename.

$filename = File::Temp::tempnam($dir,$prefix);

Equivalent to running mktemp() with $dir/$prefixXXXXXXXX
(using unix file convention as an example)

Because this function uses mktemp(), it can suffer from race conditions.

Will croak() if there is an error.

UTILITY FUNCTIONS

Useful functions for dealing with the filehandle and filename.

unlink0

Given an open filehandle and the associated filename, make a safe
unlink. This is achieved by first checking that the filename and
filehandle initially point to the same file and that the number of
links to the file is 1 (all fields returned by stat() are compared).
Then the filename is unlinked and the filehandle checked once again to
verify that the number of links on that file is now 0. This is the
closest you can come to making sure that the filename unlinked was the
same as the file whose descriptor you hold.

Returns false on error but croaks() if there is a security
anomaly. The filehandle is not closed since on some occasions this is
not required.

On some platforms, for example Windows NT, it is not possible to
unlink an open file (the file must be closed first). On those
platforms, the actual unlinking is deferred until the program ends and
good status is returned. A check is still performed to make sure that
the filehandle and filename are pointing to the same thing (but not at
the time the end block is executed since the deferred removal may not
have access to the filehandle).

Additionally, on Windows NT not all the fields returned by stat() can
be compared. For example, the dev
and rdev
fields seem to be
different. Also, it seems that the size of the file returned by stat()
does not always agree, with stat(FH) being more accurate than
stat(filename), presumably because of caching issues even when
using autoflush (this is usually overcome by waiting a while after
writing to the tempfile before attempting to unlink0
it).

Finally, on NFS file systems the link count of the file handle does
not always go to zero immediately after unlinking. Currently, this
command is expected to fail on NFS disks.

This function is disabled if the global variable $KEEP_ALL is true
and an unlink on open file is supported. If the unlink is to be deferred
to the END block, the file is still registered for removal.

This function should not be called if you are using the object oriented
interface since the it will interfere with the object destructor deleting
the file.

cmpstat

Compare stat of filehandle with stat of provided filename. This
can be used to check that the filename and filehandle initially point
to the same file and that the number of links to the file is 1 (all
fields returned by stat() are compared).

Returns false if the stat information differs or if the link count is
greater than 1. Calls croak if there is a security anomaly.

On certain platforms, for example Windows, not all the fields returned by stat()
can be compared. For example, the dev
and rdev
fields seem to be
different in Windows. Also, it seems that the size of the file
returned by stat() does not always agree, with stat(FH) being more
accurate than stat(filename), presumably because of caching issues
even when using autoflush (this is usually overcome by waiting a while
after writing to the tempfile before attempting to unlink0
it).

Not exported by default.

unlink1

Similar to unlink0
except after file comparison using cmpstat, the
filehandle is closed prior to attempting to unlink the file. This
allows the file to be removed without using an END block, but does
mean that the post-unlink comparison of the filehandle state provided
by unlink0
is not available.

Usually called from the object destructor when using the OO interface.

Not exported by default.

This function is disabled if the global variable $KEEP_ALL is true.

Can call croak() if there is a security anomaly during the stat()
comparison.

cleanup

Calling this function will cause any temp files or temp directories
that are registered for removal to be removed. This happens automatically
when the process exits but can be triggered manually if the caller is sure
that none of the temp files are required. This method can be registered as
an Apache callback.

On OSes where temp files are automatically removed when the temp file
is closed, calling this function will have no effect other than to remove
temporary directories (which may include temporary files).

File::Temp::cleanup();

Not exported by default.

PACKAGE VARIABLES

These functions control the global state of the package.

safe_level

Controls the lengths to which the module will go to check the safety of the
temporary file or directory before proceeding.
Options are:

STANDARD

Do the basic security measures to ensure the directory exists and is
writable, that temporary files are opened only if they do not already
exist, and that possible race conditions are avoided. Finally the
unlink0 function is used to remove files safely.

MEDIUM

In addition to the STANDARD security, the output directory is checked
to make sure that it is owned either by root or the user running the
program. If the directory is writable by group or by other, it is then
checked to make sure that the sticky bit is set.

Will not work on platforms that do not support the -k
test
for sticky bit.

HIGH

In addition to the MEDIUM security checks, also check for the
possibility of ``chown() giveaway'' using the POSIX
sysconf() function. If this is a possibility, each directory in the
path is checked in turn for safeness, recursively walking back to the
root directory.

For platforms that do not support the POSIX_PC_CHOWN_RESTRICTED
symbol (for example, Windows NT) it is
assumed that ``chown() giveaway'' is possible and the recursive test
is performed.

The level can be changed as follows:

File::Temp->safe_level(File::Temp::HIGH);

The level constants are not exported by the module.

Currently, you must be running at least perl v5.6.0 in order to
run with MEDIUM or HIGH security. This is simply because the
safety tests use functions from Fcntl that are not
available in older versions of perl. The problem is that the version
number for Fcntl is the same in perl 5.6.0 and in 5.005_03 even though
they are different versions.

On systems that do not support the HIGH or MEDIUM safety levels
(for example Win NT or OS/2) any attempt to change the level will
be ignored. The decision to ignore rather than raise an exception
allows portable programs to be written with high security in mind
for the systems that can support this without those programs failing
on systems where the extra tests are irrelevant.

If you really need to see whether the change has been accepted
simply examine the return value of safe_level
.

This is the highest UID on the current system that refers to a root
UID. This is used to make sure that the temporary directory is
owned by a system UID (root
, bin
, sys
etc) rather than
simply by root.

This is required since on many unix systems /tmp is not owned
by root.

Default is to assume that any UID less than or equal to 10 is a root
UID.

This value can be adjusted to reduce security checking if required.
The value is only relevant when safe_level
is set to MEDIUM or higher.

$KEEP_ALL

Controls whether temporary files and directories should be retained
regardless of any instructions in the program to remove them
automatically. This is useful for debugging but should not be used in
production code.

$File::Temp::KEEP_ALL = 1;

Default is for files to be removed as requested by the caller.

In some cases, files will only be retained if this variable is true
when the file is created. This means that you can not create a temporary
file, set this variable and expect the temp file to still be around
when the program exits.

$DEBUG

Controls whether debugging messages should be enabled.

$File::Temp::DEBUG = 1;

Default is for debugging mode to be disabled.

WARNING

For maximum security, endeavour always to avoid ever looking at,
touching, or even imputing the existence of the filename. You do not
know that that filename is connected to the same file as the handle
you have, and attempts to check this can only trigger more race
conditions. It's far more secure to use the filehandle alone and
dispense with the filename altogether.

If you need to pass the handle to something that expects a filename
then, on a unix system, use "/dev/fd/" . fileno($fh)
for arbitrary
programs, or more generally "+<=&" . fileno($fh)
for Perl
programs. You will have to clear the close-on-exec bit on that file
descriptor before passing it to another process.

Temporary files and NFS

Some problems are associated with using temporary files that reside
on NFS file systems and it is recommended that a local filesystem
is used whenever possible. Some of the security tests will most probably
fail when the temp file is not local. Additionally, be aware that
the performance of I/O operations over NFS will not be as good as for
a local disk.

Forking

In some cases files created by File::Temp are removed from within an
END block. Since END blocks are triggered when a child process exits
(unless POSIX::_exit()
is used by the child) File::Temp takes care
to only remove those temp files created by a particular process ID. This
means that a child will not attempt to remove temp files created by the
parent process.

If you are forking many processes in parallel that are all creating
temporary files, you may need to reset the random number seed using
srand(EXPR) in each child else all the children will attempt to walk
through the same set of random file names and may well cause
themselves to give up if they exceed the number of retry attempts.

Directory removal

Note that if you have chdir'ed into the temporary directory and it is
subsequently cleaned up (either in the END block or as part of object
destruction), then you will get a warning from File::Path::rmtree().

BINMODE

The file returned by File::Temp will have been opened in binary mode
if such a mode is available. If that is not correct, use the binmode()
function to change the mode of the filehandle.

Note that you can modify the encoding of a file opened by File::Temp
also by using binmode().

HISTORY

Originally began life in May 1999 as an XS interface to the system
mkstemp() function. In March 2000, the OpenBSD mkstemp() code was
translated to Perl for total control of the code's
security checking, to ensure the presence of the function regardless of
operating system and to help with portability. The module was shipped
as a standard part of perl from v5.6.1.

SEE ALSO

See File::Tempdir for an alternative object-oriented wrapper for
the tempdir
function.

AUTHOR

Tim Jenness <tjenness@cpan.org>

Copyright (C) 2007-2009 Tim Jenness.
Copyright (C) 1999-2007 Tim Jenness and the UK Particle Physics and
Astronomy Research Council. All Rights Reserved. This program is free
software; you can redistribute it and/or modify it under the same
terms as Perl itself.

Original Perl implementation loosely based on the OpenBSD C code for
mkstemp(). Thanks to Tom Christiansen for suggesting that this module
should be written and providing ideas for code improvements and
security enhancements.